중·저준위 원전 콘크리트 폐기물의 습식공정 발생 폐액 처리 및 슬러지의 필터프레스를 이용한 고액 분리에 대한 실험실 규모 평가

초록

Hundreds of thousands of tons of concrete waste are generated from decommissioned nuclear power facilities, and it has become a critical global issue to secure technology for reducing and recycling this waste. In particular, the total cost of decommissioning significantly depends on its treatment, and its volume reduction is crucial. The cost-effectiveness and overall performance of volume reduction of low- and intermediate-level radioactive concrete waste has been evaluated using the combined process of dry crushing and wet treatment (chemical dissolution using acidic solution). This study was conducted to evaluate the chemical process using coprecipitation for the treatment of acidic waste water produced by the chemical dissolution of aggregates and fine concrete powder, and subsequently, the solid-liquid separation of treated waste water containing precipitate. For the acidic waste water treatment, the optimal conditions were derived by examining the removal efficiency of simulated radionuclides, such as Co, Cs, and Sr, during the combined process of pH adjustment and addition of specific reagents (K4Fe(CN)6, BaCl2, and Na2SO4) for their coprecipitation. In the experiments on the removal of individual radionuclides, Co showed a 99.983% removal efficiency by simply increasing the pH up to 8 without the addition of any coprecipitating reagents. In comparison, Cs and Sr showed 99.999% and 99.963% removal efficiencies, respectively, with the combination of pH adjustment (increasing pH up to 8), followed by the injection of 0.003M K4Fe(CN)6 and BaSO4(0.12M BaCl2, 0.24M Na2SO4) as coprecipitating agents. Experimental results on the removal of complex radionuclides (mixed Co, Cs, and Sr) confirmed that the most significant removal of each radionuclide was achieved using the conditions (the addition of coprecipitating reagents after increasing pH up to 8) derived from the previous experiments on the individual removal, and the highest removal efficiencies of Co, Cs, and Sr were estimated to be 99.989%, 99.994% Cs, and 99.822%, respectively. In the solid-liquid separation experiment using a filter press on the wastewater generated after the removal of radionuclides using chemical treatments, it was confirmed that a pre-coated filter with 1.0 g diatomite/surface area significantly improved both volume and speed of filtration, and also the quality of treated water became better by lowering the filtrate turbidity up to 0.83 NTU. The polypropylene plain-twill weave filter was evaluated as the most relevant type for the solid-liquid separation process, as it showed the best performance in both filtration volume (797.2 mL) and filtration speed (up to 155.9 mL/min) among commercial filters tested. The result of this study is expected to contribute to reducing management costs and securing disposal space by providing an efficient treatment process for the volume reduction of low- and intermediate-level radioactive concrete waste generated during the decommissioning of nuclear power plants.

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